docs(6209): seventeen more test files — lesson shape and round trip, rule scope/moments/kind/surfacing, drift, deadlock race, backup, inception, backfill, claims, supersession, ledgers, family shapes

Docstrings and comments state the property and its reason in the present
tense. The session-context ledger test no longer describes the decision it
"used to pin"; the supersession tests state demote-not-filter without the
quote; one-row measurements become the general shape with their figures.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_lesson_document_shape.py

@@ -1,4 +1,4 @@
-"""The document a lesson is embedded as (milestone 385 step 3; milestone 427).
+"""The document a lesson is embedded as.
 
 WHY THIS IS THE STEP THAT DECIDES THE MILESTONE
 
@@ -9,17 +9,16 @@ anywhere would report that.
 
 WHERE THE SHARP SHAPE LIVES
 
-A snippet, which note #2485 measured as the only sharp record in the corpus (a
-0.153 top-to-second gap against 0.010–0.023 for everything else), is sharp
+A snippet, measured as the sharpest record kind in a corpus (a 0.153
+top-to-second gap against 0.010–0.023 for everything else), is sharp
 because its document states its purpose twice: `name — when to use` as the
 title, and again as the body's first line. A lesson follows the snippet.
 
-Until milestone 427 that `subject — trigger` title was also the STORED title,
-so every listing, menu and search row showed the trigger too — kilobytes of it.
-Now the stored title is the subject, and `embeddings.document_title` joins the
-trigger back from `data` at embed time. The embedded TEXT is what it always
-was, which is the property these guards pin: nothing re-embeds, and the floors
-tuned against these vectors stay calibrated.
+The STORED title is the subject alone, so listings, menus and search rows do
+not carry kilobytes of trigger; `embeddings.document_title` joins the trigger
+back from `data` at embed time. The embedded TEXT keeps the `subject —
+trigger` shape, which is the property these guards pin: the floors tuned
+against these vectors stay calibrated.
 
 No similarity number is asserted anywhere: a threshold pins the embedder's
 behaviour rather than this code's, and breaks on a model change that is not a
@@ -44,7 +43,7 @@ def _embedded(what: str, trigger: str, insight: str) -> tuple[str, str]:
 
 
 def test_the_stored_title_is_the_subject_alone():
-    """Milestone 427. The trigger lives in `data` and the body's first line; the
+    """The trigger lives in `data` and the body's first line; the
     title a listing shows is what the lesson is ABOUT."""
     title, _ = lessons_svc.lesson_document(SUBJECT, TRIGGER, INSIGHT)
     assert title == SUBJECT